This invention relates generally to pollution control systems and, more particularly, to a pollution control system for the removal of sulfur oxides from flue gases and the reduction of the sulfur oxides to sulfur.
It is known in the field of atmospheric pollution control to use an adsorptive process for the desulfurization of flue gases in which the sulfur-containing material is adsorbed in the porous system of an activated carbonaceous material. For example, in U.S. Pat. No. 4,219,537 adsorption is carried out in a gas-solid contacting device in which the flue gases are contacted with activated char. Sulfur dioxide in a diluted form in the gas stream passing through the activated char is adsorbed and oxidized to sulfuric acid by the oxygen and water vapor present in the gas stream.
The acid-laden or saturated char is then thermally regenerated in a regenerator, desorption vessel, or the like, by a process in which the sulfur-containing material is chemically changed in form, resulting in the decomposition of sulfuric acid to sulfur dioxide and water, whereby a portion of the carbonaceous adsorbent is oxidized to carbon dioxide. The by-product of the regeneration process is a gas stream containing 20-30% a concentrated amount of sulfur dioxide.
The SO.sub.2 -rich off-gas is usually treated further to produce elemental sulfur, which is storable and which has certain commercial applications. As taught in U.S. Pat. No. 4,147,762 the off-gas is introduced into a reactor and is reacted with crushed coal to yield gaseous elemental sulfur, which is then passed to a condenser and condensed into liquid sulfur. The liquid sulfur may be stored in appropriate containers, or may be cooled to a solid form.
In the above-described process, SO.sub.2 -rich off-gas from the regenerator contains approximately 20-30% of SO.sub.2 by volume which requires a relatively high volume of gas to be handled when compared to the amount of sulfur recovered. This relatively high volume of off-gas requires correspondingly large sized equipment, including fans, piping, valves, etc., which is expensive.